This invention relates to a membrane, and particularly although not exclusively to a membrane which may be used in an ileostomy bag to prevent faecal material contacting a gas vent and filter in the bag wall, while allowing passage of flatus gases so that these, after being deodorised by passage through the filter, can escape to atmosphere.
A membrane useful for this purpose should desirably have holes of diameter (or maximum transverse dimension in the case of a non-circular hole) in the range 1 to 10.mu., (microns). However, it is extremely difficult to make such small holes in currently available membrane films, and the thicker the film, the more difficult it is to make such small holes. However, the overall strength of the film is reduced to an undesirable level if its thickness is sufficiently small to enable holes of, say, less than 20.mu. diameter to be made by conventional methods such as needling.